1. Field of the Invention
The present invention relates to an electronic camera that captures a subject image by employing an image-capturing element.
2. Description of the Related Art
At an image-capturing element such as a CCD, electrical charges are accumulated in correspondence to the intensity of the incident subject light. However, electrical charges are also accumulated due to dark current flowing to the light-receiving elements constituting the pixels even when there is no light entering the element. Since there is inconsistency in the dark current flowing to the individual light-receiving elements, the electrical charges stored due to the dark current form a nonuniform fixed pattern among the individual pixels, Such a fixed pattern limits the sensitivity and the dynamic range of the image-capturing element, U.S. Pat. No. 5,729,288 discloses a technology for eliminating the adverse effect of stored electrical charges attributable to dark current by performing a main photographing operation in which the image-capturing element is exposed to the subject light and the resulting electrical charges are stored, as well as a shielded photographing operation in which electrical charges are stored over a length of time matching the length of the main photographing operation while the image-capturing element is shielded from the subject light. The data obtained through the shielded photographing operation is then subtracted from the data resulting from the main photographing operation.
In this technology in the related art, if the main photographing operation is executed over an extended exposure period, the shielded photographing operation needs to be performed over an equally long period of time. When the shielded photographing operation is executed over an extended period of time, electrical charges exceeding the charge storage capacity of the image-capturing element may accumulate due to the dark current, resulting in a charge overflow. In such a situation, the advantage of subtracting the shielded photographing operation data from the main photographing operation data is lost. Furthermore, the time spent executing the shielded photographing operation is wasted.